1. Field of the Invention
The invention relates to marine steering systems and, more particularly, relates to a steering system for a boat or other watercraft that is powered by a motor and steered with a tiller. Specifically, the system includes a tiller-operated power assist steering system that imposes steering forces on the watercraft""s motor or other steered element upon tiller actuation.
2. Discussion of the Related Art
In one type of conventional marine steering system, a watercraft such as a boat is steered by pivoting an outboard motor on the stern of the watercraft about a vertical steering axis under control of an operator. The steering forces are typically generated manually using a tiller that is located at the stem of the boat and that is connected to the motor either directly or indirectly via a mechanical steering linkage.
Manually operated tillers of the type described above are very effective for steering boats equipped with small and mid-sized outboard motors. However, they exhibit some drawbacks and disadvantages, particularly in applications equipped with relatively large motors. For instance, the forces required to steer the boat increase at least generally proportionately with motor size. Relatively large outboard motors, i.e., 150 horsepower motors and larger, can therefore be difficult to steer manually using a standard tiller. In fact, a 225 horsepower motor would typically require a tiller that is 4xe2x80x2 to 5xe2x80x2 long to permit comfortable manual steering. Tillers of that length are not practical in most boats. Relatively large outboard motors therefore are typically steered using power assist steering systems controlled by a steering wheel located at the helm of the boat rather than by using a tiller located at the stem of the boat. This remote steering requirement adds considerable cost and complexity to the typical boat.
Another problem associated with the typical tiller steered boat is that reaction forces are imposed on and by the motor during its operation that cause the steering angle to change unless the reaction forces are countered by the operator. The operator must therefore retain control of the tiller at all times in order to maintain a desired heading. The operator""s freedom of movement therefore is sharply curtailed. In addition, the reaction forces, like the steering forces, increase generally proportionately with motor size. The relatively large reaction forces imposed on and by larger motors require commensurately larger retention forces by the operator, leading to operator fatigue over time.
The need therefore has arisen to provide a tiller operated power assist steering system that reduces the level of effort required by an operator to steer a boat or other watercraft.
The need has additionally arisen to provide a tiller operated power assist steering system that maintains a steering angle against reaction forces on or by the steered element, thereby negating the need for the operator to constantly man the tiller.
In accordance with a first aspect of the invention, a power assist steering assist system for a tiller-steerable watercraft includes a tiller which is configured to be operatively coupled to the steered element, an actuator, and a drive mechanism such that tiller movement effects actuation of the drive mechanism to impose power-assisted steering forces on the steered element. Preferably, the tiller is also mechanically or otherwise operatively coupled to the steered element so as to impose manually-generated steering forces on the steered element upon manipulation of the tiller in a first manner and to effect actuation of the drive mechanism to impose power-assisted steering forces on the steered element upon tiller manipulation in a second manner.
The tiller preferably comprises an actuator portion which is movable relative to the remainder of the tiller. In this case, the tiller cooperates with the actuator and is configured to cooperate with the steered element such that the tiller operates in the first manner when the tiller moves as a unit and operates in the second manner when the actuator portion moves relative to the remainder of the tiller. The actuator portion may, for example, be an articulating outer end portion of a tiller arm of the tiller or a movable throttle grip mounted on the tiller.
The steering system may be a hydraulic power assist steering system, in which case the drive mechanism preferably comprises an unbalanced steering cylinder assembly and the actuator comprises a hydraulic actuator that will typically include a control valve assembly that is controlled by operation of the tiller in the first manner to control the flow of hydraulic fluid to and form the steering cylinder assembly. The hydraulic actuator preferably comprises a control valve assembly that is mechanically coupled to the actuator portion of the tiller so as to control fluid flow between the steering cylinder and a pump and between the steering cylinder and a reservoir in response to movement of the actuator portion of the tiller relative to the remainder of the tiller.
Regardless of the drive mechanism and actuator employed, a biasing arrangement preferably is provided in the tiller to bias the actuator portion to a neutral position in which the drive mechanism is locked, e.g., through the closure of valves controlling hydraulic fluid flow to and from a steering cylinder. This locking resists steered element movement which could otherwise occur through the imposition of reaction forces on or by the motor, permitting the operator to release the tiller and perform other activities.
In accordance with another aspect of the invention, a method of steering a watercraft comprises moving a first portion of a tiller relative to a second portion of the tiller to operate a drive mechanism so as to impose power assist steering forces on a steered element of a watercraft. In order to permit manual steering to supplement the power assist steering forces or to substitute for those forces in the event of failure of the power assist steering system, the method preferably further comprises moving the first and second portions of the tiller as a unit to impose manually-generated steering forces on the steered element.
The moving step resulting in the imposition of hydraulic assist steering forces may comprise pivoting an outer portion of a tiller arm of the tiller relative to an inner portion of the tiller arm. Alternatively, it may comprise pivoting a throttle shaft of the tiller relative to a tiller arm on which the throttle shaft is mounted. In either event, the power steering forces may be hydraulically-generated power assist steering forces imposed on the steered element by directing hydraulic fluid to and from a steering cylinder assembly which is mechanically coupled to the steered element. These hydraulically generated steering forces may be generated using pressurized hydraulic fluid.